The ignition timing can be adjusted in accord with the octane of the fuel used. With a Foxwell NT510 Elite this is done by following this menu path from the ME 2.8 motor electronics main menu:
Special functions -> Correction Programming -> Ignition
Using DAS (Star Diagnosis) the path is similar:
Control unit adaptations -> Correction programming -> ignition
Select the octane of the fuel you are using: 89, 91, or 93. The ignition timing will retard for lower octane fuel and advance for higher octane. In this manner an incremental performance gain can be had by selecting higher octane, or a savings of money at the pump can be had by selecting lower. If I’m not mistaken U.S. cars are delivered with the octane set for 91 fuel.
For your information, here in the Eastern U.S. the difference in price between 89 octane and 93 is ~35 cents per gallon. I myself post the most expensive fuel — 93 octane — but I know M-B owners who prefer to save some money and pump a lower grade. For those owners it makes sense to set the ignition maps for the lower grade.
Car is Benz R230 2003 — 2012
Credits to @ bobterry99